Use of thiazolyl-pyridinium based dyes in optical layers for optical data recording

ABSTRACT

The present invention relates to the use of thiazolyl-pyridinium based dyes in optical layers for optical data recording, preferably for optical data recording using a laser with a wavelength up to 450 nm. 
     The invention further relates to a write only read many (WORM) type optical data recording medium capable of recording and reproducing information with radiation of blue laser, which employs a thiazolyl-pyridinium based type dye in the optical layer. 
     The present invention further relates to new thiazolyl-pyridinium based dyes, of formula (V), (VI) or (VIII).

The present invention relates to the use of thiazolyl-pyridinium baseddyes in optical layers for optical data recording, preferably foroptical data recording using a laser with a wavelength up to 450 nm.

The invention further relates to a write only read many (WORM) typeoptical recording medium capable of recording and reproducinginformation with radiation of blue laser, which employs athiazolyl-pyridinium based dye in the optical layer.

The present invention further relates to new thiazolyl-pyridinium baseddye compounds.

Recently, organic dyes have attracted considerable attentions in thefield of diode-laser optical storage. Commercial recordable compactdiscs (CD-R) and recordable digital versatile discs (DVD-R) can contain,as recording layer, numerous dyes based on phthalocyanine, hemicyanine,cyanine and metallized azo structures. These dyes are suitable in theirrespective fields with the laser wavelength criteria. Other generalrequirements for dye media are strong absorption, high reflectance, highrecording sensitivity, low thermal conductivity as well as light andthermal stabilities, durability for storage or non-toxicity.

For industrial application, these dyes have to be suitable for the spincoating process to prepare thin films, i.e. they have to be sufficientlysoluble in the organic solvents generally applied in the spin coatingprocess.

WORM (write once read many) type and erasable type optical recordingmedia reproduce information by detecting variations in the reflectivitycaused by physical deformation, by alterations of opticalcharacteristics as well as by phase and magnetic properties of arecording layer before and after the recording.

Recordable compact discs (CD-R) are widely known as a WORM type opticalrecording medium. Recently, digital versatile discs (DVD) with increasedinformation storage capabilities up to 4.7 GBytes have beencommercialized.

The DVD-R technology adopts as a light source a red diode laser with awavelength of 630-670 nm. Thereby the pit size and track interval can bereduced, increasing the information storage capacity by up to 6-8 timescompared to CD-R's.

Blu-ray® discs (Blu-ray® disc is a standard developed by Hitachi Ltd.,LG Electronics Inc., Matsushita Electric Industrial Co. Ltd., PioneerCorporation, Royal Philips Electronics, Samsung Electronics Co. Ltd.,Sharp Corporation, Sony Corporation, Thomson Multimedia) are going to bethe next milestone in optical recording technology. Its newspecification increases the data storage up to 27 GBytes per recordinglayer for a 12 cm diameter disc. By adopting a blue diode laser with awavelength of 405 nm (GaN or SHG laser diodes), the pit size and trackinterval can be further reduced, again increasing the storage capacityby an order of magnitude.

The construction of optical data recording media is known in the art. Anoptical data recording media generally comprises a substrate and arecording layer, the optical layer. Usually discs or wavers of organicpolymeric materials are used as substrates. Preferred substrates arepolycarbonate (PC) or polymethylmethacrylate (PMMA). The substrate hasto provide an even and uniform surface of high optical quality. Theoptical layer is deposited thereon in a thin and uniform film of highoptical quality and defined thickness. Finally, a reflective layer, e.g.aluminium, gold or copper, is deposited upon the optical layer.

Advanced optical data recording media may comprise further layers, suchas protective layers, adhesive layers or additional optical layers.

To provide for a thin and uniform film of the optical layer, thematerial is usually deposited by spin coating, vacuum evaporation, jetcoating, rolling coating or soaking. The preferred process in industryis spin coating to form an optical layer of about 70 nm to 250 nmthickness. For the application in the spin coating process, the materialof the optical layer has to be highly soluble in organic solvents.

DE 1795369 and U.S. Pat. No. 3,703,577 (American Cyanamid Company)disclose compounds of the following formula, in particularthiazolyl-pyridinium salts and oxazolyl-pyridinium salts, theirsynthesis and the use of these compounds for the lowering of bloodglucose levels in warm blooded animals.

U.S. Pat. No. 4,571,402 (Schering Corporation) discloses2-(4′-pyridinyl)-thiazole derivatives, in particular carboxylates,carboxamides and thiocarboxamides, their preparation and their use asbronchodilating agents.

Kerr et al. (J. Am. Chem. Soc. 82, 1960, 186) describe the saltformation of substituted oxazoles and thiazoles.

Wallenfels et al. (Justus Liebigs Ann. Chem. 621, 1959, 198) describethe synthesis of 1-(2,6-dichlorobenzyl)-4-[thiazolyl(2)]-pyridiniumbromides.

Surprisingly it has been found, that thiazolyl-pyridinium based dyes asdescribed below are useful as dye compounds in optical layers foroptical data recording media.

The present invention therefore relates to the use ofthiazolyl-pyridinium based dyes in an optical layer comprisingthiazolyl-pyridinium based dyes as described below and to the use ofsaid optical layers for optical data recording media.

More particularly, the invention relates to a write once read many(WORM) type optical data recording medium capable of recording andreproducing information with radiation of blue laser of preferably 405nm, which employs a thiazolyl-pyridinium based dye in the optical layer

The invention further relates to new thiazolyl-pyridinium based dyecompounds.

The present invention is directed to an optical layer comprising atleast one dye compound of formulae (I) or (II)

wherein

-   R₁ represents a represents a linear or branched C₁₋₂ alkyl,-   R₂ to R₅ independently of one another, represent hydrogen, cyano    (—CN), halogen, nitro (NO₂), hydroxy, C₁₋₈ alkoxy (—OR) wherein the    alkyl (R) can be unsubstituted or substituted by C₁₋₈ alkyl, hydroxy    (—OH), by CH₆₋₁₂ aryl or by —NR₈R₉ in which R₈ and R₉ are    independently hydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl;    -   C₁₋₈ alkyl, wherein the alkyl can be unsubstituted or        substituted by C₁₋₈ alkyl, hydroxy (—OH), by CH₆₋₁₂ aryl or by        —NR₈R₉ in which R₈ and R₉ are independently hydrogen, C₁₋₈ alkyl        or C₆₋₁₂ aryl;    -   CX₃ where X can be chlorine, fluorine, bromine;    -   C₁₋₈ alkylthio, wherein the alkyl can be unsubstituted or        substituted by C₁₋₈ alkyl, hydroxy (—OH), by CH₆₋₁₂ aryl or by        —NR₈R₉ in which R₈ and R₉ are independently hydrogen, C₁₋₈ alkyl        or C₆₋₁₂ aryl;-   R₂ and R₃,-   R₄ and R₅,-   R₃ and R₄ (only for (II)) can form a saturated or insaturated    homocyclic or heterocyclic five-membered or six-membered ring which    may additionally contain oxygen or further nitrogen as a ring    member.-   R₆ and R₇ independently of one another, represent hydrogen, cyano    (—CN), halogen, nitro (NO₂), hydroxy, linear or branched C₁₋₈ alkoxy    (—OR) wherein the alkyl (R) can be unsubstituted or substituted by    C₁₋₈ alkyl, hydroxy (—OH), by CH₆₋₁₂ aryl or by —NR₈R₉ in which R₈    and R₉ are independently hydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl;    -   linear or branched C₁₋₈ alkyl, wherein the alkyl can be        unsubstituted or substituted by C₁₋₈ alkyl, hydroxy (—OH), by        CH₆₋₁₂ aryl or by —NR₈R₉ in which R₈ and R₉ are independently        hydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl;    -   CX₃ where X can be chlorine, fluorine, bromine;    -   linear or branched C₁₋₈ alkylthio, wherein the alkyl can be        unsubstituted or substituted by C₁₋₈ alkyl, hydroxy (—OH), by        C₆₋₁₂ aryl or by —NR₈R₉ in which R₈ and R₉ are independently        hydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl;    -   C₆-C₁₂ aryl, which is unsubstituted or substituted by C₁₋₈        alkyl, hydroxy (—OH), nitro (NO₂), cyano (—CN), halogen, by        CH₆₋₁₂ aryl, by —NR₈R₉ in which R₈ and R₉ are independently        hydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl or by C₁-C₈ alkoxy (—OR); or-   R₆ and R₇ can form a homocyclic six-membered ring to give a compound    of formula (I) or (II) which is represented by formula (III) or (IV)

-   -   in which R₁₀-R₁₃ independently of one another represent        hydrogen, cyano (—CN), halogen, nitro (NO₂), hydroxy, C₁₋₈        alkoxy (—OR) wherein the alkyl (R) can be unsubstituted or        substituted by C₁₋₈ alkyl, hydroxy (—OH), by C₆₋₁₂ aryl or by        —NR₈R₉ in which R₈ and R₉ are independently hydrogen, C₁₋₈ alkyl        or C₆₋₁₂ aryl;    -   C₁₋₈ alkyl, wherein the alkyl can be unsubstituted or        substituted by C₁₋₈ alkyl, hydroxy (—OH), by CH₆₋₁₂ aryl or by        —NR₈R₉ in which R₈ and R₉ are independently hydrogen, C₁₋₈ alkyl        or C₆₋₁₂ aryl;    -   CX₃ where X can be chlorine, fluorine, bromine;    -   C₁₋₈ alkylthio, wherein the alkyl can be unsubstituted or        substituted by C₁₋₈ alkyl, hydroxy (—OH), by C₆₋₁₂ aryl or by        —NR₈R₉ in which R₈ and R₉ are independently hydrogen, C₁₋₈ alkyl        or C₆₋₁₂ aryl;

-   An- represents an anion counter-part selected from inorganic anions    such as iodine, fluorine, bromine, chlorine, perchlorate,    hexafluoroantimonate, hexafluorophosphate, tetrafluoroborate,    tetraphenylborate or organic anions such as dicyanoamide (N(CN)₂) or    trifluoromethanesulfonimide (N(SO₂CF₃)₂; or

-   An⁻ can also be an anionic azo metal complex based on cobalt metal.

In a preferred aspect, the present invention is directed to an opticallayer comprising at least one dye compound of formulae (I) or (II)wherein

-   R₁ represents a represents a linear or branched C₁₋₁₂ alkyl,-   R₂ to R₅ independently of one another, represent hydrogen, cyano    (—CN), halogen, nitro (NO₂), hydroxy, C₁₋₈ alkoxy (—OR) wherein the    alkyl (R) can be unsubstituted or substituted by C₁₋₈ alkyl, hydroxy    (—OH), by C₆₋₁₂ aryl or by —NR₈R₉ in which R₈ and R₉ are    independently hydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl;    -   C₁₋₈ alkyl, wherein the alkyl can be unsubstituted or        substituted by C₁₋₈ alkyl, hydroxy (—OH), by CH₆₋₁₂ aryl or by        —NR₈R₉ in which R₈ and R₉ are independently hydrogen, C₁₋₈ alkyl        or C₆₋₁₂ aryl;    -   CX₃ where X can be chlorine, fluorine, bromine;    -   C₁₋₈ alkylthio, wherein the alkyl can be unsubstituted or        substituted by C₁₋₈ alkyl, hydroxy (—OH), by C₆₋₁₂ aryl or by        —NR₈R₉ in which R₈ and R₉ are independently hydrogen, C₁₋₈ alkyl        or C₆₋₁₂ aryl;-   R₂ and R₃,-   R₄ and R₅, can form a saturated or insaturated homocyclic or    heterocyclic five-membered or six-membered ring which may    additionally contain oxygen or further nitrogen as a ring member.-   R₆ and R₇ independently of one another, represent hydrogen, cyano    (—CN), halogen, nitro (NO₂), hydroxy, linear or branched C₁₋₈ alkoxy    (—OR) wherein the alkyl (R) can be unsubstituted or substituted by    C₁₋₈ alkyl, hydroxy (—OH), by C₆₋₁₂ aryl or by —NR₈R₉ in which R₈    and R₉ are independently hydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl;    -   linear or branched C₁₋₈ alkyl, wherein the alkyl can be        unsubstituted or substituted by C₁₋₈ alkyl, hydroxy (—OH), by        C₆₋₁₂ aryl or by —NR₈R₉ in which R₈ and R₉ are independently        hydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl;    -   CX₃ where X can be chlorine, fluorine, bromine;    -   C₆-C₁₂ aryl, which is unsubstituted or substituted by C₁₋₈        alkyl, hydroxy (—OH), nitro (NO₂), cyano (—CN), halogen, by        C₆₋₁₂ aryl, by —NR₈R₉ in which R₈ and R₉ are independently        hydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl or by C₁-C₈ alkoxy (—OR); or-   R₆ and R₇ can form a homocyclic six-membered ring to give a compound    of formula (I) or (II) which is represented by formula (III) or (IV)    as above, in which R₁₀-R₁₃ independently of one another represent    hydrogen, cyano (—CN), halogen, nitro (NO₂), hydroxy, C₁₋₈ alkoxy    (—OR) wherein the alkyl (R) can be unsubstituted or substituted by    C₁₋₈ alkyl, hydroxy (—OH), by C₆₋₁₂ aryl or by —NR₈R₉ in which R₈    and R₉ are independently hydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl;    -   C₁₋₈ alkyl, wherein the alkyl can be unsubstituted or        substituted by C₁₋₈ alkyl, hydroxy (—OH), by CH₆₋₁₂ aryl or by        —NR₈R₉ in which R₈ and R₉ are independently hydrogen, C₁₋₈ alkyl        or C₆₋₁₂ aryl;    -   CX₃ where X can be chlorine, fluorine, bromine;-   An- represents an anion counter-part selected from inorganic anions    such as iodine, fluorine, bromine, chlorine, perchlorate,    hexafluoroantimonate, hexafluorophosphate, tetrafluoroborate,    tetraphenylborate or organic anions such as dicyanoamide (N(CN)₂) or    trifluoromethanesulfonimide (N(SO₂CF₃)₂; or-   An⁻ can also be an anionic azo metal complex based on cobalt metal.

In a more preferred aspect, the present invention is directed to anoptical layer comprising at least one dye compound of formulae (I) or(II), wherein

-   R₁ represents a represents a linear or branched C₁₋₆ alkyl,-   R₂ to R₅ represent hydrogen,-   R₆ represents hydrogen, cyano (—CN), halogen, nitro (NO₂), hydroxy,    linear or branched C₁₋₈ alkoxy (—OR) wherein the alkyl (R) can be    unsubstituted or substituted by C₁₋₈ alkyl, hydroxy (—OH), by CH₆₋₁₂    aryl or by —NR₈R₉ in which R₈ and R₉ are independently hydrogen,    C₁₋₈ alkyl or C₆₋₁₂ aryl;    -   linear or branched C₁₋₈ alkyl, wherein the alkyl can be        unsubstituted or substituted by C₁₋₈ alkyl, hydroxy (—OH), by        CH₆₋₁₂ aryl or by —NR₈R₉ in which R₈ and R₉ are independently        hydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl;    -   CX₃ where X can be chlorine, fluorine, bromine;    -   C₆-C₁₂ aryl, which is unsubstituted or substituted by C₁₋₈        alkyl, hydroxy (—OH), nitro (NO₂), cyano (—CN), halogen, by        CH₆₋₁₂ aryl, by —NR₈R₉ in which R₈ and R₉ are independently        hydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl or by C₁-C₈ alkoxy (—OR)-   R₇ represents hydrogen or-   R₆ and R₇ can form a homocyclic six-membered ring to give a compound    of formula (I) or (II) which is represented by formula (III) or (IV)    as above, in which R₁₀-R₁₃ independently of one another represent    hydrogen, cyano (—CN), halogen, C₁₋₈ alkyl, wherein the alkyl can be    unsubstituted or substituted by C₁₋₈ alkyl, hydroxy (—OH), by C₆₋₁₂    aryl or by —NR₈R₉ in which R₈ and R₉ are independently hydrogen,    C₁₋₈ alkyl or C₆₋₁₂ aryl;-   An- represents an anion counter-part selected from inorganic anions    such as iodine, fluorine, bromine, chlorine, perchlorate,    hexafluoroantimonate, hexafluorophosphate, tetrafluoroborate; or-   An⁻ can also be an anionic azo metal complex based on cobalt metal.

In a most preferred embodiment, the present invention is directed to anoptical layer comprising a dye compound of formula (I), wherein

-   R₁ represents a linear or branched C₁₋₆ alkyl,-   R₂ to R₅ represent hydrogen,-   R₆ represents hydrogen, methyl, ethyl, phenyl, 4-methoxyphenyl, tert    butyl, trifluoromethyl,-   R₇ represents hydrogen, or-   R₆ and R₇ can form a homocyclic six-membered ring to give a compound    of formula (I) which is represented by formula (III) as above, in    which R₁₀, R₁₂ and R₁₃ represent hydrogen and R₁₁ represents methyl    or chlorine,-   An- represents an anion counter-part selected from inorganic anions    such as iodine, chlorine, perchlorate, hexafluoroantimonate,    hexafluorophosphate, tetrafluoroborate, or an anionic azo cobalt    complex of the following formula

An optical layer according to the invention may also comprise a mixtureof two or more, preferably of two dye compounds of formula (I) or (II)as defined above.

The thiazolyl-pyridinium based dye compounds of formula (I) or (II)provide for particularity preferable properties when used in opticallayers for optical data recording media according to the invention.

In a further aspect the invention relates to new thiazolyl-pyridiniumbased dye compounds of formula (V) or (VI)

wherein

-   R¹ is selected from methyl, ethyl, n- or i-propyl;-   R₆ is selected from tert.butyl, methoxy or CF₃;-   An- is defined as above;    as well as to the compounds of formula (VII) or (VIII)

wherein

-   R₁ is selected from methyl, ethyl, n- or i-propyl;-   R₁₁ is selected from hydrogen, cyano (—CN), C₁₋₈alkyl (preferably    methyl), halogen (preferably Cl);-   An- is defined as above.

Further, the invention relates to a method for producing optical layerscomprising the following steps

-   -   (a) providing a substrate,    -   (b) dissolving a dye compound or a mixture of dye compounds of        formula (I) or (II) in an organic solvent to form a solution,    -   (c) coating the solution (b) on the substrate (a);    -   (d) evaporating the solvent to form a dye layer.

Preferred substrates are polycarbonate (PC) or polymethylmethacrylate(PMMA).

Organic solvents are selected from C₁₋₈ alcohol , halogen substitutedC₁₋₈ alcohols, C₁₋₈ ketone, C₁₋₈ ether, halogen substituted C₁₋₄ alkane,or amides.

Preferred C₁₋₈ alcohols or halogen substituted C₁₋₈ alcohols are forexample methanol, ethanol, isopropanol, diacetone alcohol (DAA),2,2,3,3-tetrafluoropropanol, trichloroethanol, 2-chloroethanol,octafluoropentanol or hexafluorobutanol.

Preferred C₁₋₈ ketones are for example acetone, methylisobutylketone,methylethylketone, or 3-hydroxy-3-methyl-2-butanone.

Preferred halogen substituted C₁₋₄ alkanes are for example chloroform,dichloromethane or 1-chlorobutane.

Preferred amides are for example dimethylformamide or dimethylacetamide.

The optical layer (dye layer) obtained preferably has a thickness from70 to 250 nm.

In a preferred aspect, the present invention provides for an opticallayer suitable for high-density recording material, e.g. of the WORMdisc format, in a laser wavelength range of from 350-450 nm, preferablyaround 405 nm.

The dye compounds of formula (I) or (II) possess the required opticalcharacteristics (such as high absortivity, high recording sensitivity asexample), an excellent solubility in organic solvents, an excellentlight stability and a decomposition temperature of 250-300° C.

Preparation of Thiazolyl-Pyridinium Based Type Dyes According to theInvention

The thiazolyl-pyridinium based dye compounds of formula (I) and (II) areobtained by reacting a pyridine-4-thioamide (A) or apyridine-2-thioamide (B), respectively, with a alpha-haloketone (F) in apolar solvent in a ratio of 1:1 to get (G) or (H) respectively, followedby reacting the substituted pyridine moiety with an alkylating agent ina polar solvent. Anion exchange is performed on compound (I) or (II) inan inert solvent under reflux condition with the correspondingcounter-ion suitable for the exchange.

The preparation of benzothiazolylpyridinium based dye compounds may alsobe carried out by reacting pyridine-4-carbaldehyde (C) orpyridine-2-carbaldehyde (D), respectively with an o-hydroxyaniline zincsalt of formula (E) in a polar solvent in a ratio of 1:1 to get (K) or(L) respectively, followed by reacting the substituted pyridine moietywith an alkylating agent in a polar solvent.

wherein R₂ to R₁₃ and An- are defined as above. X represents halogen.

The process for the preparation of dyes of formula (I) and (II) can bedescribed by the following steps:

-   -   (a) a reaction between (A) or (B) or (C) or (D) and (E) or (F)        to form the thiazolylpyridine (G) or (H) or (K) or (L).    -   (b) an alkylation reaction of the thiazolylpyridine (G) or (H)        or (K) or (L) using a slight excess of alkylating agent leading        to the dye (I) or (II) respectively    -   (c) An anion exchange on compound (I) or (II) using an inert        solvent and a suitable counter-ion.

The preferred solvent of the condensation step (step (a)) of (A) or (B)or (C) or (D) and (E) or (F) is selected from the group consisting ofketones (acetone, methylethylketone), alcohols (methanol, ethanol,1-propanol, 2-propanol) or halogenated solvents (dichloromethane,trichloromethane).

The preferred solvent for the step (b) is selected from the groupconsisting of ketones (acetone, methylethylketone), halogenated solvents(dichloromethane, dichloroethane), dimethylformamide (DMF),N-methylpyrolidone (NMP).

The most preferred solvents for step (c) are methylethylketone,dichloromethane, acetonitrile or 2-propanole.

Preparation of an Optical Layer

An optical layer according to the invention comprises a dye of formula(I) or (II) or a mixture of dyes of formula (I) or (II).

A method for producing an optical layer according to the inventioncomprises the following steps

-   (a) Providing a substrate,-   (b) Dissolving a dye compound or a mixture of dye compounds of    formula (I) or (II) in an organic solvent to form a solution,-   (c) Coating the solution (b) on the substrate (a);-   (d) Evaporating the solvent to form a dye layer.    Preparing of the High Density Optical Recording Medium

A method for producing an optical recording medium comprising an opticallayer according to the invention comprises the following additionalsteps

-   (e) sputtering a metal layer onto the dye layer-   (f) applying a second polymer based layer to complete the disk.

A high-density data storage medium according to the invention thereforepreferably is a recordable optical disc comprising: a first substrate,which is a transparent substrate with grooves, a recording layer(optical layer), which is formed on the first substrate surface usingthe dye of formula (I) or (II), a reflective layer formed on therecording layer, a second substrate, which is a transparent substratewith grooves connected to the reflective layer with an attachment layer.

The dyes of formula (I) or (II) in the form of a solid film have a highrefractive index at the longer wavelength flank of the absorption band,which preferably achieves a peak value of from 2.0 to 3.0 in the rangeof from 350 to 500 nm. The dyes of formula (I) or (II) allow providing amedium having high reflectivity as well as high sensitivity and goodplayback characteristics in the desired spectral range.

(a) Substrate

The substrate, which functions as support for the layers appliedthereto, is advantageously semi-transparent (T>10%) or preferablytransparent (T>90%). The support can have a thickness of from 0.01 to 10mm, preferably from 0.1 to 5 mm.

Suitable substrates are, for example, glass, minerals, ceramics andthermosetting or thermoplastic plastics. Preferred supports are glassand homo- or co-polymeric plastics. Suitable plastics are, for example,thermoplastic polycarbonates, polyamides, polyesters, polyacrylates andpolymethacrylates, polyurethanes, polyolefins, polyvinyl chloride,polyvinylidene fluoride, polyimides, thermosetting polyesters and epoxyresins.

The most preferred substrates are polycarbonate (PC) orpolymethylmethacrylate (PMMA).

The substrate can be in pure form or may also comprise customaryadditives, for example UV absorbers or dyes, as proposed e.g. in JP04/167239 as light-stabilizers for the recording layer. In the lattercase it may be advantageous for the dye added to the support substrateto have an absorption maximum hypso-chromically shifted relative to thedye of the recording layer by at least 10 nm, preferably by at least 20nm.

The substrate is advantageously transparent over at least a portion ofthe range from 350 to 500 nm, so that it is permeable to at least 90% ofthe incident light of the writing or readout wavelength.

(b) Organic Solvents

Organic solvents are selected from C₁₋₈ alcohol, halogen substitutedC₁₋₈ alcohols, C₁₋₈ ketone, C₁₋₈ ether, halogen substituted C₁₋₄ alkane,or amides.

Preferred C₁₋₈ alcohols or halogen substituted C₁₋₈ alcohols are forexample methanol, ethanol, isopropanol, diacetone alcohol (DAA),2,2,3,3-tetrafluoropropanol, trichloroethanol, 2-chloroethanol,octafluoropentanol or hexafluorobutanol.

Preferred C₁₋₈ ketones are for example acetone, methylisobutylketone,methylethylketone, or 3-hydroxy-3-methyl-2-butanone.

Preferred halogen substituted C₁₋₄ alkanes are for example chloroform,dichloromethane or 1-chlorobutane.

Preferred amides are for example dimethylformamide or dimethylacetamide.

(c) Recording Layer

The recording layer (optical layer) is preferably arranged between thetransparent substrate and the reflecting layer. The thickness of therecording layer is from 10 to 1000 nm, preferably from 30 to 300 nm,especially about 80 nm, for example from 60 to 120 nm.

The use of dyes of formula (I) or (II) results in advantageouslyhomogeneous, amorphous and low-scattering recording layers having a highrefractive index. The absorption edge is surprisingly steep even in thesolid phase. Further advantages are high light stability in daylight andunder laser radiation of low power density with, at the same time, highsensitivity under laser radiation of high power density, uniform scriptwidth, high contrast, and also good thermal stability and storagestability.

The recording layer, instead of comprising a single compound of formula(I) or (II), may also comprise a mixture of such compounds according tothe invention. By the use of mixtures, for example mixtures of isomersor homologues as well as mixtures of different structures, thesolubility can often be increased and/or the amorphous content improved.

For a further increase in stability it is also possible, if desired, toadd known stabilizers in customary amounts, for example a nickeldithiolate as light stabilizer, as described in JP 04/025493.

The recording layer comprises a compound of formula (I) or (II) or amixture of such compounds preferably in an amount sufficient to have asubstantial influence on the refractive index, for example at least 30%by weight, more preferably at least 60% by weight, most preferably atleast 80% by weight.

Further customary components are, for example other chromophores (forexample those disclosed in W0-01/75873, or others having an absorptionmaximum at from 300 to 1000 nm), stabilizers, ¹0₂-, triplet- orluminescence quenchers, melting-point reducers, decompositionaccelerators or any other additives that have already been described inoptical recording media. Preferably, stabilizers orfluorescence-quenchers are added if desired.

When the recording layer comprises further chromophores, they may inprinciple be any dye that can be decomposed or modified by the laserradiation during the recording, or they may be inert towards the laserradiation. When the further chromophores are decomposed or modified bythe laser radiation, this can take place directly by absorption of thelaser radiation or can be induced indirectly by the decomposition of thecompounds of formula (I) or (II) according to the invention, for examplethermally.

Naturally, further chromophores or colored stabilizers may influence theoptical properties of the recording layer. It is therefore preferable touse further chromophores or coloured stabilizers, the optical propertiesof which conform as far as possible to those of the compounds formula(I) or (II) or are as different as possible, or the amount of furtherchromophores is kept small.

When further chromophores having optical properties that conform as faras possible to those of compounds formula (I) or (II) are used,preferably this should be the case in the range of thelongest-wavelength absorption flank. Preferably the wavelengths of theinversion points of the further chromophores and of the compounds offormula (I) and (II) are a maximum of 20 nm, especially a maximum of 10nm, apart. In that case the further chromophores and the compounds offormula (I) or (II) should exhibit similar behavior in respect of thelaser radiation, so that it is possible to use as further chromophoresknown recording agents the action of which is synergistically enhancedby the compounds of formula (I) or (II).

When further chromophores or colored stabilizers having opticalproperties that are as different as possible from those of compounds offormula (I) or (II) are used, they advantageously have an absorptionmaximum that is hypso-chromically or batho-chromically shifted relativeto the dye of formula (I) or (II). In that case the absorption maximaare preferably at least 50 nm, especially at least 100 nm, apart.

Examples thereof are UV absorbers that are hypso-chromic to the dye offormula (I) or (II) or colored stabilizers that are bathochromic to thedye of formula (I) or (II) and have absorption maxima lying, forexample, in the NIR or IR range.

Other dyes can also be added for the purpose of color-codedidentification, color-masking (“diamond dyes”) or enhancing theaesthetic appearance of the recording layer. In all those cases, thefurther chromophores or colored stabilizers should preferably exhibitbehavior towards light and laser radiation that is as inert as possible.

When another dye is added in order to modify the optical properties ofthe compounds of formula (I) or (II), the amount thereof is dependentupon the optical properties to be achieved. The person skilled in theart will find little difficulty in varying the ratio of additional dyeto compound of formula (I) or (II) until he obtains his desired result.

When chromophores or colored stabilizers are used for other purposes,the amount thereof should preferably be small so that their contributionto the total absorption of the recording layer in the range of from 350to 500 nm is a maximum of 20%, preferably a maximum of 10%. In such acase, the amount of additional dye or stabilizer is advantageously amaximum of 50% by weight, preferably a maximum of 10% by weight, basedon the recording layer.

Further chromophores that can be used in the recording layer in additionto the compounds of formula (I) or (II) are described in the followingpatents

Applicant Patent Application No. Ricoh JP2002283722, JP2003094824,JP200283732, JP2003063139 Mitsubishi JP2003019867, JP2001271001,JP2002036727, JP2001181524, JP2003170662, JP2003237233, JP2002002110,JP2003103935, JP2003127542 Ciba WO02/082438 Sony WO02/102598 KabushikiEP1149873 Bayer WO02/084656, WO02080152 Ciba WO03/063151 FEW ChemicalsDE10109243 Mitsui Chem WO03035407, WO03039882, JP2003165273,JP2004082439, JP2003103932, JP2003074282, JP2003072238, JP2003211847,JP2002363437, WO03082593, JP2003286415, JP2003140300, JP2003266947,JP2002264520, JP2004090372, JP2004142131 Sony Corp./Bayer AG WO03030158Bayer AG DE10245581, WO03079339 Fuji Photo Film Co Ltd JP2003075961,JP2003040851, EP1345217, JP2003211848 US2003180496, JP2003246141,JP2003211852, EP1193699, JP2004131396, JP2004050612 Nippon Kayaku KKJP2003170663 Asashi Denka JP2001047740, JP2004034645 Taiyo YudenJP2003191641 Nippon Kayaku KK JP2003246142 Canon U.S. Pat. No. 4,804,613Matsushita JP2003266938 Shanghai Precision Opt. CN1438221 Instr. Inst.

Most preferably, however, no additional chromophore is added, unless itis a colored stabilizer.

Stabilizers, ¹0₂-, triplet- or luminescence-quenchers are, for example,metal complexes of N- or S-containing enolates, phenolates,bisphenolates, thiolates or bisthiolates or of azo, azomethine orformazan dyes, such as bis(4-dimethylaminodithiobenzil)nickel [CAS N^(o)38465-55.3]. Hindered phenols and derivatives thereof such aso-hydroxyphenyl-triazoles or -triazines or other UV absorbers, such ashindered amines (TEMPO or HALS, as well as nitroxides or NOR-HALS), andalso as cations diimmonium, Paraquat or Orthoquat salts, such as®Kayasorb IRG 022, ®Kayasorb IRG 040, optionally also as radical ions,such as N,N,N′,N′-tetrakis(4-dibutylaminophenyl)-p-phenyleneamine-ammonium hexafluorophosphate, hexafluoroantimonate or perchlorate.The latter are available from Organica (Wolfen/DE); ®Kayasorb brands areavailable from Nippon Kayaku Co. Ltd.

The person skilled in the art will know from other optical informationmedia, or will easily identify, which additives in which concentrationare best suited to which purpose. Suitable concentrations of additivesare, for example, from 0.001 to 1000% by weight, preferably from 1 to 50(% by weight, based on the recording medium of formula (II)).

(e) Reflecting Layer

Reflecting materials suitable for the reflective layer includeespecially metals, which provide good reflection of the laser radiationused for recording and playback, for example the metals of Main GroupsIII, IV and V and of the Sub-groups of the Periodic Table of theElements. Al, In, Sn, Pb, Sb, Bi, Cu, Ag, Au, Zn, Cd, Hg, Sc, Y, La, Ti,Zr, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Ce,Pr, Nd, Pm, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm, Yb and Lu and alloys thereofare especially suitable. Special preference is given to a reflectivelayer of aluminum, silver, copper, gold or an alloy thereof, on accountof their high reflectivity and ease of production.

(f) Cover Layer/Protective Layer

Materials suitable for the cover layer/protective layer includeplastics, which are applied in a thin layer to the support or theuppermost layer either directly or with the aid of adhesive layers. Itis advantageous to select mechanically and thermally stable plasticshaving good surface properties, which may be modified further.

The plastics may be thermosetting plastics and thermoplastic plastics.Preference is given to radiation-cured (e.g. using UV radiation)protective layers, which are particularly simple and economical toproduce. A wide variety of radiation-curable materials are known.Examples of radiation-curable monomers and oligomers are acrylates andmethacrylates of diols, triols and tetrols, polyimides of aromatictetracarboxylic acids and aromatic diamines having C₁-C₄ alkyl groups inat least two ortho-positions of the amino groups, and oligomers withdialkylmaleinimidyl groups, e.g. dimethyl maleinimidyl groups.

The recording media according to the invention may also have additionallayers, for example interference layers. It is also possible toconstruct recording media having a plurality of (for example two)recording layers. The structure and the use of such materials are knownto the person skilled in the art. Preferred, if present, areinterference layers that are arranged between the recording layer andthe reflecting layer and/or between the recording layer and thesubstrate and consist of a dielectric material, for example as describedin EP 0353393 of TiO₂, Si₃N₄, ZnS or silicone resins.

The recording media according to the invention can be produced byprocesses known in the art.

Coating Methods

Suitable coating methods are, for example, immersion, pouring,brush-coating, blade-application and spin-coating, as well asvapor-deposition methods carried out under a high vacuum. When pouringmethods are used, solutions in organic solvents are generally used. Whensolvents are employed, care should be taken that the supports used areinsensitive to those solvents. Suitable coating methods and solvents aredescribed, for example, in EP-A-401 791.

The recording layer is preferably applied by spin-coating with a dyesolution, solvents that have proved satisfactory are preferablyalcohols, e.g. 2-methoxyethanol, n-propanol, isopropanol, isobutanol,n-butanol, amyl alcohol or 3-methyl-1-butanol or preferably fluorinatedalcohols, e.g. 2,2,2-trifluoroethanol or 2,2,3,3-tetrafluoro-1-propanol,octafluoropentanol and mixtures thereof. It will be understood thatother solvents or solvent mixtures can also be used, for example thosesolvent mixtures described in EP-A-511 598 and EP-A-833 316. Ethers(dibutyl ether), ketones (2,6-dimethyl-4-heptanone, 5-methyl-2-hexanone)or saturated or unsaturated hydrocarbons (toluene, xylene) can also beused, for example in the form of mixtures (e.g. dibutylether/2,6-dimethyl-4-heptanone) or mixed components.

The person skilled in the art of spin-coating will in general routinelytry out all the solvents with which is he is familiar, as well as binaryand ternary mixtures thereof, in order to discover the solvents orsolvent mixtures which result in a high-quality and, at the same time,cost-effective recording layer containing the solid components of hischoice. Known methods of process engineering can also be employed insuch optimization procedures, so that the number of experiments to becarried out can be kept to a minimum.

The invention therefore relates also to a method of producing an opticalrecording medium, wherein a solution of a compound of formula (I) or(II) in an organic solvent is applied to a substrate having pits. Theapplication is preferably carried out by spin-coating.

The application of the metallic reflective layer is preferably effectedby sputtering, vapor-deposition in vacuum or by chemical vapordeposition (CVD). The sputtering technique is especially preferred forthe application of the metallic reflective layer on account of the highdegree of adhesion to the support. Such techniques are known and aredescribed in specialist literature (e.g. J. L. Vossen and W. Kern, “ThinFilm Processes”, Academic Press, 1978).

Readout Methods

The structure of the recording medium according to the invention isgoverned primarily by the readout method; known function principlesinclude the measurement of the change in the transmission or,preferably, in the reflection, but it is also known to measure, forexample, the fluorescence instead of the transmission or reflection.

When the recording material is structured for a change in reflection,the following structures, can be used: transparent support/recordinglayer (optionally multilayered)/reflective layer and, if expedient,protective layer (not necessarily transparent); or support (notnecessarily transparent)/reflective layer/recording layer and, ifexpedient, transparent protective layer. In the first case, the light isincident from the support side, whereas in the latter case the radiationis incident from the recording layer side or, where applicable, from theprotective layer side. In both cases the light detector is located onthe same side as the light source. The first-mentioned structure of therecording material to be used according to the invention is generallypreferred.

When the recording material is structured for a change in lighttransmission, the following different structure comes intoconsideration: transparent support/recording layer (optionallymultilayered) and, if expedient, transparent protective layer. The lightfor recording and for readout can be incident either from the supportside or from the recording layer side or, where applicable, from theprotective layer side, the light detector in this case always beinglocated on the opposite side.

Suitable lasers are those having a wavelength of 350-500 nm, for examplecommercially available lasers having a wavelength of 405 to 414 nm,especially semi-conductor lasers. The recording is done, for example,point for point, by modulating the laser in accordance with the marklengths and focusing its radiation onto the recording layer. It is knownfrom the specialist literature that other methods are currently beingdeveloped which may also be suitable for use.

The process according to the invention allows the storage of informationwith great reliability and stability, distinguished by very goodmechanical and thermal stability and by high light stability and bysharp boundary zones of the pits. Special advantages include the highcontrast, the low jitter and the surprisingly high signal/noise ratio,so that excellent readout is achieved.

The readout of information is carried out according to methods known inthe art by registering the change in absorption or reflection usinglaser radiation, for example as described in “CD-Player and R-DATRecorder” (Claus Biaesch-Wiepke, Vogel Buchverlag, Würzburg 1992).

The optical recording medium according to the invention is preferably arecordable optical disc of the WORM type. It may be used, for example,as a playable HD-DVD (high density digital versatile disc) or Blu-ray®disc, as storage medium for a computer or as an identification andsecurity card or for the production of diffractive optical elements, forexample holograms.

The invention accordingly relates also to a method for the opticalrecording, storage and playback of information, wherein a recordingmedium according to the invention is used. The recording and theplayback advantageously take place in a wavelength range of from 350 to500 nm.

It has been found, that the new dyes of formula (I) or (II) according tothe invention enhance the photosensitivity and the stability to lightand heat compared to dyes already known in the art. The new dyes offormula (I) or (II) according to the invention have a decompositiontemperature of 250-350° C. Additionally, these compounds show anextremely good solubility in organic solvents, which is ideal for thespin-coating process to manufacture optical layers.

Thus, it is of great advantage to use these new compounds in therecording layer of high-density recordable optical discs.

EXAMPLES

All thiazolyl-pyridinium based dye compounds were prepared usingstandard procedures known in the art, in particular using reactions asdescribed above.

In the following examples “part” is always part by weight unlessindicated otherwise.

Example 1

13 parts of pyridine-4-thioamide are suspended in 195 parts of ethanol.20 parts or 2-bromoacetophenone are added and the mixture is refluxedfor 5 h. The crude product is filtered, treated with 79 parts ofacetone, filtered at 40° C. and dried at 80° C. under vacuo. 100 partsof aqueous ammonia (13%) are added, the mixture stirred 30 min. at roomtemperature, the product filtered and washed with water. Afterwards, theproduct is recrystallized from 250 parts of aqueous methanol (70%). 15parts of 4-[4-phenyl-thiazolyl-(2)]pyridine are obtained as beigecrystals.

Example 2-4

The following compounds are synthesized according to the proceduresdescribed for example 1.

Example 2

Example 3

Example 4

Example 5

20 parts of 2-amino-5-methylthiophenol zinc salt are refluxed in 315parts of acetic acid and treated with 12.5 partspyridine-4-carbaldehyde. After 15 min. the mixture is cooled to roomtemperature, added to 600 parts of water and stirred for 1 h. Theproduct is filtered and washed with water to yield 22 parts of6-methyl-2-pyridin-4-yl-benzothiazole.

Example 6

6-chlor-2-pyridin-4-yl-benzothiazole is synthesized according to theprocedure described for example 5.

Example 7

20 parts of the compound obtained in example 1 and 15 parts of2-iodopropane are refluxed in 158 parts of acetone for 2 h. At roomtemperature, 500 parts of ethyl acetate are added and the precipitatefiltered to obtain 0.7 parts of1-isopropyl-4-[4-phenyl-thiazolyl-(2)]-pyridiniumiodide.

UV-Vis (MeOH) λ_(max): 373 nm; ∈ (λ_(max)): 31 L·g⁻¹·cm⁻¹; solubility(in tetrafluoropropanol, 20° C.): >50 g/L; TGA (decomp.)=270° C.; MS(positive mode): 281 (M⁺), (negative mode): 127 (I⁻).

Example 8

85 parts of the compound obtained in example 2, 277 parts of iodomethaneand 1200 parts of 2-butanone are stirred for 8h at 100° C. in a pressurevessel. The product is filtered, washed with ethyl acetate and dried toobtain 111 parts of1-methyl-4-[4-tert-butyl-thiazolyl-(2)]-pyridiniumiodide.

UV-Vis (MeOH) λ_(max): 359 nm; ∈ (λ_(max)): 56 L·g⁻¹·cm⁻¹; solubility(in 2,2,3,3-tetrafluoropropanol, 20° C.): >50 μg/L; ¹H-NMR (500 MHz,CDCl₃) δ=1.40 (9H), 4.71 (3H), 7.35 (1H), 8.46 (2H), 9.35 (2H).

Example 9-11

The following compounds are synthesized according to the proceduresdescribed for example 8.

Example 9

Starting with a compound of example 1 to yield1-methyl-4-[4-phenyl-thiazolyl-(2)]-pyridinium iodide

UV-Vis (MeOH) λ_(max): 389 nm; ∈ (λ_(max)) 32 L·g⁻¹·cm⁻¹; solubility (in2,2,3,3-tetrafluoropropanol, 20° C.): >30 g/L; TGA (decomp.)=260° C.;¹H-NMR (500 MHz, D₆-DMSO) δ=4.37 (3H), 7.46 (1H), 7.53 (2H), 8.12 (2H),8.68 (3H), 9.07 (2H).

Example 10

Starting with a compound of example 3 to yield4-[4-(4-methoxy-phenyl)-thiazol-2-yl]-1-methyl-pyridinium iodide

UV-Vis (MeOH) λ_(max): 403 nm; ∈ (λ_(max)): 18.3 L·g⁻¹·cm⁻¹; solubility(in 2,2,3,3-tetrafluoropropanol, 20° C.): >50 g/L; TGA (decomp.)=250°C.; ¹H-NMR (500 MHz, D₆-DMSO) δ=3.83 (3H), 4.37 (3H), 7.07 (2H), 8.05(2H), 8.52 (1H), 8.66 (2H), 9.05 (2H)

Example 11

Starting with a compound of example 3 to yield 1-isopropyl-4-[4-(4-methoxy-phenyl)-thiazol-2-yl]-1-methyl-pyridinium iodide

UV-Vis (MeOH) λ_(max): 405 nm; ∈ (λ_(max)): 19.4 L·g⁻¹·cm⁻¹; solubility(in 2,2,3,3-tetrafluoropropanol, 20° C.): >50 g/L; TGA (decomp.)=240°C.; ¹H-NMR (500 MHz, D₆-DMSO) δ=1.65 (6H), 3.83 (3H), 5.07 (1H), 7.08(2H), 8.06 (2H), 8.53 (1H), 8.66 (2H), 9.25 (2H).

Example 12

10 parts of the compound obtained in example 6 and 7 parts ofdimethylsulfate are stirred at 100° C. for 30 minutes. At roomtemperature, 100 parts of water and 12 parts of potassium iodide areadded and the product filtered. The product is washed with water anddried to yield 11 parts of1-methyl-4-(6-chlor-benzothiazol-2-yl)pyridinium iodide.

UV-Vis (MeOH) λ_(max): 351 nm; ∈ (λ_(max)): 46 L·g⁻¹·cm⁻¹; solubility(in 2,2,3,3-tetrafluoropropanol, 20° C.): >50 g/L; TGA (decomp.)=244°C.; ¹H-NMR (500 MHz, D₆-DMSO) δ=4.41 (3H), 7.74 (1H), 8.26 (1H), 8.55(1H), 8.75 (2H), 9.13 (2H).

Example 13

2.5 parts of 1-methyl-4-[4-tert-butyl-thiazolyl-(2)]-pyridiniumiodide ofexample 8 and 6.3 parts of cobalt complex with triethylammonium ascounter-ion are mixed into 50 parts of acetonitrile. The mixture is thenstirred at reflux for 12 hours. The mixture is cooled to 25° C.,filtered and washed with acetonitrile. The marroon presscake is driedand the final dye is obtained with 95% yield.

UV-Vis (CH2Cl2) λ_(max): 512 nm; ∈ (λ_(max)): 55.0 L·g⁻¹·cm⁻¹;Solubility (in Tetrafluoropropanol, 25° C.): 20 g/l; DSC (decomp.)=341°C.; Heat release (W/g)=15; On spin coated disc: n_((405nm))=1.61,k_((405nm))=0.26.

Example 14

2.0 parts 1-methyl-4-[4-phenyl-thiazolyl-(2)]-pyridinium iodide ofexample 9 and 7.2 parts of cobalt complex with triethylammonium ascounter-ion are mixed into 50 parts of acetonitrile. The mixture is thenstirred at reflux for 12 hours. The mixture is cooled to 25° C.,filtered and washed with acetonitrile. The marroon presscake is driedand the final dye is obtained with 90% yield.

UV-Vis (CH2Cl2) λ_(max): 479 nm; ∈ (λ_(max)): 50 L·g⁻¹·cm⁻¹; Solubility(in Tetrafluoropropanol, 25° C.): 20 g/L; DSC (decomp.)=322° C.; Heatrelease (W/g)=6; On spin coated disc: n_((405nm))=1.58,k_((405nm))=0.34.

Application Example

The optical and thermal properties of the thiazolyl-pyridinium based dyecompounds were studied. The dyes show high absorption at the desiredwavelengths. In addition, the shape of the absorption spectra, thatstill remains critical to the disc reflectivity and formation of cleanmark edges, are composed of one major band, comprised in a range of from350 to 500 nm, preferably of from 350 to 400 nm.

More precisely, n values of the refractive index were evaluated between1.0 and 2.7 (see examples 13, 14). Light stabilities were foundcomparable to commercial dyes which usually are stabilised withquenchers for the use in optical data recording.

Sharp threshold of thermal decomposition within the required temperaturerange characterizes the new thiazolylpyridinium based dyes which areassumed to be desirable for the application in optical layers foroptical data recording.

As a conclusion, the thiazolyl-pyridinium based dye compounds are withinthe specifications which are primarily required by the industry for theuse of dyes in optical data recording, in particular in thenext-generation optical data recording media in the blue laser range.

1. An optical layer comprising at least one dye compound of formula (I)or (II)

wherein R1 is a linear or branched C₁₋₁₂ alkyl, R2 to R5 independentlyof one another, are hydrogen, cyano (—CN), halogen, nitro (NO₂),hydroxy, C₁₋₈ alkoxy (—OR) wherein (R) is alkyl which is unsubstitutedor substituted by C₁₋₈ alkyl, hydroxy (—OH), C₆₋₁₂ aryl or —NR8R9,wherein R8 and R9 are independently hydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl;C₁₋₈ alkyl, wherein the alkyl is unsubstituted or substituted by C₁₋₈alkyl, hydroxy (—OH), C₆₋₁₂ aryl or —NR8R9, wherein R8 and R9 areindependently hydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl; CX3 where X ischlorine, fluorine or bromine; C₁₋₈ alkylthio, wherein the alkyl isunsubstituted or substituted by C₁₋₈ alkyl, hydroxy (—OH), C₆₋₁₂ aryl orby —NR8R9, wherein R8 and R9 are independently hydrogen, C₁₋₈ alkyl orC₆₋₁₂ aryl; or wherein, for formula (I), R2 and R3, or R4 and R5, form asaturated or unsaturated homocyclic or heterocyclic five-membered orsix-membered ring optionally containing oxygen or an additional nitrogenas a ring member; or wherein, for formula (II) R2 and R3, R4 and R5, orR3 and R4 form a saturated or unsaturated homocyclic or heterocyclicfive-membered or six-membered ring optionally containing oxygen or anadditional nitrogen as a ring member; R6 and R7 independently of oneanother, are hydrogen, cyano (—CN), halogen, nitro (NO₂), hydroxy,linear or branched C₁₋₈ alkoxy (—OR) wherein (R) is alkyl which isunsubstituted or substituted by C₁₋₈ alkyl, hydroxy (—OH), C₆₋₁₂ aryl or—NR8R9, wherein R8 and R9 are independently hydrogen, C₁₋₈ alkyl orC₆₋₁₂ aryl; linear or branched C₁₋₈ alkyl, wherein the alkyl isunsubstituted or substituted by C₁₋₈ alkyl, hydroxy (—OH), C₆₋₁₂ aryl or—NR8R9, wherein R8 and R9 are independently hydrogen, C₁₋₈ alkyl orC₆₋₁₂ aryl; CX₃ where X is chlorine, fluorine or bromine; linear orbranched C₁₋₈ alkylthio, wherein the alkyl is unsubstituted orsubstituted by C₁₋₈ alkyl, hydroxy (—OH), C₆₋₁₂ aryl or —NR8R9, whereinR8 and R9 are independently hydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl; C₆-C₁₂aryl, unsubstituted or substituted by C₁₋₈ alkyl, hydroxy (—OH), nitro(NO₂), cyano (—CN), halogen, C₆₋₁₂ aryl, —NR8R9, wherein R8 and R9 areindependently hydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl or C₁-C₈ alkoxy (—OR);or R6 and R7 form a homocyclic six-membered ring to give a compound offormula (I) or (II) represented by formula (III) or (IV)

wherein R10-R13 independently of one another represent hydrogen, cyano(—CN), halogen, nitro (NO₂), hydroxy, C₁₋₈ alkoxy (—OR) wherein thealkyl (R) is unsubstituted or substituted by C₁₋₈ alkyl, hydroxy (—OH),C₆₋₁₂ aryl or —NR8R9, wherein R8 and R9 are independently hydrogen, C₁₋₈alkyl or C₆₋₁₂ aryl; C₁₋₈ alkyl, wherein the alkyl is unsubstituted orsubstituted by C₁₋₈ alkyl, hydroxy (—OH), C₆₋₁₂ aryl or —NR8R9, whereinR8 and R9 are independently hydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl; CX3where X is chlorine, fluorine or bromine; C₁₋₈ alkylthio, wherein thealkyl is unsubstituted or substituted by C₁₋₈ alkyl, hydroxy (—OH),C₆-C₁₂ aryl or —NR8R9, wherein R8 and R9 are independently hydrogen,C₁₋₈ alkyl or C₆₋₁₂ aryl; An- is an anionic azo metal complex of thefollowing formula


2. An optical layer according to claim 1, wherein R1 is a linear orbranched C₁₋₁₂ alkyl, R2 to R5 independently of one another, arehydrogen, cyano (—CN), halogen, nitro (NO₂), hydroxy, C₁₋₈ alkoxy (—OR)wherein (R) is alkyl which is unsubstituted or substituted by C₁₋₈alkyl, hydroxy (—OH), C₆₋₁₂ aryl or —NR8R9, wherein R8 and R9 areindependently hydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl; C₁₋₈ alkyl, whereinthe alkyl is unsubstituted or substituted by C₁₋₈ alkyl, hydroxy (—OH),C₆₋₁₂ aryl or —NR8R9, wherein R8 and R9 are independently hydrogen, C₁₋₈alkyl or C₆₋₁₂ aryl; CX3 where X is chlorine, fluorine or bromine; C₁₋₈alkylthio, wherein the alkyl is unsubstituted or substituted by C₁₋₈alkyl, hydroxy (—OH), C₆₋₁₂ aryl or —NR8R9, wherein R8 and R9 areindependently hydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl; or wherein R2 and R3,or R4 and R5, form a saturated or unsaturated homocyclic or heterocyclicfive-membered or six-membered ring, optionally oxygen or an additionnitrogen as a ring member; R6 and R7 independently of one another, arehydrogen, cyano (—CN), halogen, nitro (NO₂), hydroxy, linear or branchedC₁₋₈ alkoxy (—OR) wherein (R) is alkyl which is unsubstituted orsubstituted by C₁₋₈ alkyl, hydroxy (—OH), C₆₋₁₂ aryl or —NR8R9, whereinR8 and R9 are independently hydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl; linearor branched C₁₋₈ alkyl, wherein the alkyl is unsubstituted orsubstituted by C₁₋₈ alkyl, hydroxy (—OH), C₆₋₁₂ aryl or —NR8R9, whereinR8 and R9 are independently hydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl; CX3where X is chlorine, fluorine or bromine; C₆-C₁₂ aryl, unsubstituted orsubstituted by C₁₋₈ alkyl, hydroxy (—OH), nitro (NO₂), cyano (—CN),halogen, C₆₋₁₂ aryl, or —NR8R9, wherein R8 and R9 are independentlyhydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl or C₁-C₈ alkoxy (—OR); or R6 and R7can form a homocyclic six-membered ring to give a compound of formula(I) or (II) represented by formula (III) or (IV) as defined in claim 1,wherein R10-R13 independently of one another are hydrogen, cyano (—CN),halogen, nitro (NO₂), hydroxy, C₁₋₈ alkoxy (—OR) wherein (R) is alkylwhich is unsubstituted or substituted by C₁₋₈ alkyl, hydroxy (—OH),C₆₋₁₂ aryl or —NR8R9, wherein R8 and R9 are independently hydrogen, C₁₋₈alkyl or C₆₋₁₂ aryl; C₁₋₈ alkyl, wherein the alkyl is unsubstituted orsubstituted by C₁₋₈ alkyl, hydroxy (—OH), C₆₋₁₂ aryl or —NR8R9, whereinR8 and R9 are independently hydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl; CX3where X is chlorine, fluorine or bromine; An- is as defined in claim 1.3. An optical layer according to claim 1, wherein R1 is a linear orbranched C₁₋₆ alkyl, R2 to R5 are hydrogen, R6 is hydrogen, cyano (—CN),halogen, nitro (NO₂), hydroxy, linear or branched C₁₋₈ alkoxy (—OR)wherein the alkyl (R) is unsubstituted or substituted by C₁₋₈ alkyl,hydroxy (—OH), C₆₋₁₂ aryl or —NR8R9, wherein R8 and R9 are independentlyhydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl; linear or branched C₁₋₈ alkyl,wherein the alkyl is unsubstituted or substituted by C₁₋₈ alkyl, hydroxy(—OH), C₆₋₁₂ aryl or —NR8R9, wherein R8 and R9 are independentlyhydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl; CX3 where X is chlorine, fluorine orbromine; C₆-C₁₂ aryl, unsubstituted or substituted by C₁₋₈ alkyl,hydroxy (—OH), nitro (NO₂), cyano (—CN), halogen, C₆₋₁₂ aryl, —NR8R9,wherein R8 and R9 are independently hydrogen, C₁₋₈ alkyl or C₆₋₁₂ arylor C₁-C₈ alkoxy (—OR) R7 is hydrogen or R6 and R7 form a homocyclicsix-membered ring to give a compound of formula (I) or (II) representedby formula (III) or (IV) as defined in claim 1, wherein R10-R13independently of one another are hydrogen, cyano (—CN), halogen, C₁₋₈alkyl, wherein the alkyl is unsubstituted or substituted by C₁₋₈ alkyl,hydroxy (—OH), C₆₋₁₂ aryl or —NR8R9, wherein R8 and R9 are independentlyhydrogen, C₁₋₈ alkyl or C₆₋₁₂ aryl; An- is as defined in claim
 1. 4. Anoptical layer according to claim 1, wherein the dye compound is offormula (I), and R1 is a linear or branched C₁₋₆ alkyl R2 to R5 arehydrogen, R6 is hydrogen, methyl, ethyl, phenyl, 4-methoxyphenyl,tert-butyl or trifluoromethyl, R7 is hydrogen, or R6 and R7 form ahomocyclic six-membered ring to give a compound of formula (I)represented by formula (III) as defined in claim 1, wherein R10, R12 andR13 are hydrogen and R11 is methyl or chlorine, An- is as defined inclaim
 1. 5. An optical layer comprising a mixture of at least two dyecompounds according to formula (I) or formula (II) as defined inclaim
 1. 6. A method for producing an optical layer according to claim1, comprising the steps of (a) providing a substrate (a), (b) dissolvinga dye compound or a mixture of dye compounds of formula (I) or (II) asdefined in claim 1 in an organic solvent to form a solution (b), (c)coating the solution (b) on the substrate (a); (d) evaporating thesolvent to form a dye layer.
 7. A method according to claim 6, whereinthe substrate is polycarbonate (PC) or polymethylmethacrylate (PMMA). 8.A method according to claim 6, wherein the organic solvent is selectedfrom the group consisting of C₁₋₈ alcohol, halogen substituted C₁₋₈alcohols, C₁₋₈ ketone, C₁₋₈ ether, halogen substituted C₁₋₄ alkane, andamides.
 9. An optical recording medium comprising an optical layeraccording to claim
 5. 10. An optical layer according to claim 1, whereinAn- is an inorganic anion selected from the group consisting of iodine,fluorine, bromine, chlorine, perchlorate, hexafluoroantimonate,hexafluorophosphate, tetrafluoroborate and tetraphenylborate.
 11. Anoptical layer according to claim 1, wherein An- is an organic anionselected from the group consisting of dicyanoamide (N(CN)₂) ortrifluoromethanesulfonimide (N(SO₂CF₃)₂.
 12. An optical layer accordingto claim 3, wherein An- is an inorganic anion selected from the groupconsisting of iodine, fluorine, bromine, chlorine, perchlorate,hexafluoroantimonate, hexafluorophosphate, tetrafluoroborate andtetraphenylborate.
 13. An optical layer according to claim 3, whereinAn- is an inorganic cation selected from the group consisting of iodine,chlorine, perchlorate, hexafluoroantimonate, hexafluorophosphate andtetrafluoroborate.
 14. An optical recording medium comprising an opticallayer according to claim
 1. 15. A dye compound of formula (VI),

wherein R1 is selected from methyl, ethyl, n- and i-propyl; R6 ismethoxy or CF₃; and An- is an anion counter-part selected from the groupconsisting of inorganic anions, organic anions and an anionic azo metalcomplex based on cobalt metal.
 16. A dye compound of formula (VI)according to claim 15, wherein An- is an inorganic anion selected fromthe group consisting of iodine, fluorine, bromine, chlorine,perchlorate, hexafluoroantimonate, hexafluorophosphate,tetrafluoroborate and tetraphenylborate.
 17. A dye compound of formula(VI) according to claim 15, wherein An- is an inorganic cation selectedfrom the group consisting of iodine, chlorine, perchlorate,hexafluoroantimonate, hexafluorophosphate and tetrafluoroborate.
 18. Adye compound of formula (VIII),

wherein R1 is selected from methyl, ethyl, n- or i-propyl; R11 is cyano;An- is an anion counter-part selected from the group consisting ofinorganic anions, organic anions and an anionic azo metal complex basedon cobalt metal.
 19. A dye compound of formula (VIII), according toclaim 18, wherein An- is an inorganic anion selected from the groupconsisting of iodine, fluorine, bromine, chlorine, perchlorate,hexafluoroantimonate, hexafluorophosphate, tetrafluoroborate andtetraphenylborate.
 20. A dye compound of formula (VIII), according toclaim 18, wherein An- is an inorganic cation selected from the groupconsisting of iodine, chlorine, perchlorate, hexafluoroantimonate,hexafluorophosphate and tetrafluoroborate.